Psychological stress has been linked to the development of hypertension (HTN) but the process by which this occurs is poorly understood. Prolonged blood pressure (BP) responses to stress have been shown to increase risk for HTN, and there is growing evidence indicating that thinking about stressful experiences, in addition to experiencing them directly, can affect BP. Thus, it has been hypothesized that engaging in perseverative cognitions about past or future stressors may contribute to prolonged physiological activation and, over time, the development of HTN. Evidence that perseverative cognitions are associated with delayed BP recovery and impaired sleep quality, which both increase HTN risk, provides preliminary support for the hypothesis. However, progress in this emerging field has been limited by several important conceptual and methodological issues. Little is known about the nature of perseverative cognition in the real world: how much do people ruminate about stressful events, what factors influence the likelihood of engaging in such thoughts, and what are their effects on sleep and BP? Also, to be considered as a possible risk factor, it must be demonstrated that individual differences in perseverative cognition exist and are stable over time. These questions can best be addressed using ecological momentary assessment (EMA). The goal of the proposed R21 is to resolve these issues in preparation for a future application in which we will conduct a larger, more intensive study to formally test the hypothesized model. We will conduct an EMA study in which a diverse sample of 163 normotensive and untreated hypertensive subjects will undergo electronic diary-based assessment of daily stress exposure and perseverative cognitions, actigraphy and ambulatory BP monitoring over a 2-week period. The aims are: (1) To determine the feasibility of using an extended EMA protocol to simultaneously assess stress exposure, perseverative cognitions, sleep quality and BP in the natural environment; (2) To quantify subjects' exposure to daily stress and their experience of perseverative cognitions and explore whether these differ according to situational and/or person-level factors; (3) To assess the stability of stress exposure and perseverative cognitions over a 2-week period, and to estimate the duration of monitoring required to reliably assess each; and (4) To conduct exploratory analyses of associations of daily stress and perseverative cognitions with sleep quality and BP, which will provide effect size estimates to inform future studies. Public Health Significance: More than 28% of the U.S. population has HTN, which continues to be a major cause of morbidity and mortality. Psychological stress increases HTN risk, and understanding the mechanisms involved may lead to improved interventions. This study will address important gaps in the literature and provide critical information for the design of a larger study to determine the role of perseverative cognition in the relationships between stress, impaired sleep and elevated BP. The findings will also be broadly applicable to the design of investigations of other health effects of stress and stress-related thoughts.